Preparation Of Starch Pearls By Disc Granulation And Quality Improvement

Starch pearls,also known as "powder balls" and "Boba",are spherical food made of starch and water through the granulation process.Cooked starch pearls are highly transparent,good elasticity and chewing,usually eaten with tea and milk to provide a unique taste.Starch pearls originated in Asia and became popular in Europe and United States.However,the research on starch pearls is still scarce,and there is no mature and standardized granulation process.Manual is still used in some studies,which is not commensurate with its popularity.Therefore,this paper aims to explore the feasibility of using disk granulation technology to prepare high quality starch pearls,in order to provide a new technical solution for the research and production of starch pearls.Focusing on the above goals,this paper carries out three parts of research content.Firstly,the feasibility of preparing starch pearl by disk granulation and the effect of starch structure and physicochemical properties were discussed in this study.Secondly,the feasibility of adding inulin to improve the quality of starch pearls and the effect of inulin polymerization degree were discussed.Finally,the feasibility of improving the quality of starch pearls by adding pre-gelatinization process and the influence of pregelatinization degree were discussed.The main conclusions are as follows:(1)Nine representative starches(amylose content 1.96%～67.05%)from cereals,tubers,and legumes were selected as raw powders to produce starch pearls by disc granulation.Nine kinds of starch powder can be made into starch pearls,but high straight chain and waxy corn starch pearls were not resistant to cooking.Cluster and Pearson correlation analysis further indicated that to produce starch pearls with high granule strength and good cooking qualities,the selected starch preferably had the following characteristics:1.a lower amylose content(ranged from 25.90%～41.56%in this study).2.a lower pasting temperature.3.a higher ratio of amylopectin extra-long chains(DP≥36)to amylopectin short chains(DP 6～12).4.a larger particle size.Overall,potato and cassava starches were the most suitable among the nine starches for the production of starch pearls by disc granulation.(2)Inulin could interact with starch in hydrogen bond,compete with starch for water,inhibit the swelling of starch particles and improve the water solubility of powder,so as to improve the granular strength and cooking quality of tapioca pearls.Inulin with low degree of polymerization(DP≤10)has the stronger hydrogen bond interaction with starch and forms a stronger gel network structure,so it is best to add the low polymerization inulin.The addition 3%(w/w)of low polymerization inulin significantly reduced the friction loss(1.96%to 1.04%)and cooking loss(47.80%to 43.55%)of tapioca pearls.It also significantly improved its transparency(9.44%to 12.61%),volume expansion(4.87 to 7.00),hardness(483 to 674 g)and chewiness(202 to 299 g).The addition of medium degree inulin(DP 2～60)and high degree inulin(DP≥23)had adverse effects on the transparency,breaking force or cooking loss.(3)Pre-gelatinization will reduce the enthalpy of gelatinization,increase the gelatinization temperature and enhance the gel structure of tapioca starch pearls,so as to improve the granular strength and cooking quality of tapioca starch pearls.When the pre-gelatinization degree is 54%,the quality of tapioca starch pearls is the best.At this degree,the granular strength(82 to 9194 g),hardness(578 to 714 g),elastic(0.66 to 0.85)and chewiness(364 to 463 g)of tapioca pearls were significantly improved.Friction losses(18.92%to 1.97%)and cooking losses(64.46%to 47.38%)were significantly reduced,while the color and clarity were visually unaffected.When the pre-gelatinization degree is 4%,the granular strength of tapioca pearls had low granular strength(174.67%)and high cooking loss(62.43%).When the pre-gelatinization degree was higher than 85%,the brightness and transparency of tapioca pearls decrease significantly,and the yellow degree increased significantly.In conclusion,disk granulation is a feasible means to prepare starch pearls.The quality of starch pearls can be significantly improved by selecting appropriate starch,adding appropriate ingredients and pre-gelatinizing process.In this study,selecting cassava or potato starch as raw material,adding inulin with low polymerization and adding about 50%degree of gelatinization is beneficial to prepare starch pearls with good granular strength,cooking quality and texture.